Synodontids are widely distributed in coastal waters of the Persian Gulf . The reproductive features of this fish were poorly studied. There are only fragmentary data on the reproductive biology of Saurida tumbil in Hendijan region. The purpose of this work was to elucidate some features of the sexual cycle, fecundity, nature and spawning period of this most common species of the family Synodontidae in the Persian Gulf . Samples of Saurida tumbil were collected from the commercial catches at Bushehr fishery harbor from February 2007 to February 2008, by regular monthly collections. A total of 691 specimens, including 39 immature, 114 males and 538 females were collected. The total length (in mm), as well as, the total weight (in g) of the fish were recorded. After carring out biometrical measurments, the fish were dissected and gonads were removed, weighted to the nearest milligram and thoroughly examined for determination of its sex and maturity stage. The gonadosomatic index was calculated as the percentage of gonad weight to the total body weight. For histological examination, pieces of the gonads were fixed in 10% formalin. Then, they were passed through an ascending series of ethylalcohol, cleared in xylene and embedded in paraffin wax (59? c). Sections of 5-7 µm thick were stained with Eosin hematoxylin for microscopic examinations. The total length of mature fish ranged from 26.1 to 58 cm in females and from 25.5 to 53.5 cm in males. The weight of mature fish ranged from 136 to 1550 g in females and from 116 to 1125 g in males. The slope line ( b ) in the length-weight equation for all fish was 3.042 and for immature was 3.35, suggesting an isometric and allometric growth, respectively. Condition factor ranged from 0.67 to 0.79 in different months. The gut content consisted mostly of fish species and the relative length of gut (RLG) was 0.44, on average, suggesting a carnivorous feeding habit. Amongst the 691 studied fish, 187 had empty and 504 had full stomachs. Clupeids, carangids and trichiurids were the most preferred preys in the full stomachs. Monthly distribution of GSI for female and male Saurida tumbil, showed that the GSI values have two peaks, the first and the maximum was in May and the second and smaller peak was in October. The minimum GSI for the two sexes was in December. The GSI of females and males fluctuated similarly. It was found that female and male Saurida tumbil reach the first sexual maturity at 27 and 25.5 cm, respectively. Mean absolute and relative fecundity was 263162 and 273, respectively. The minimum and maximum ova diameter was 6.71µ (stage 1) and 875.34µ (stage 5). The curvilinear relationship between the fecundity and total weight of the fish was F=2657.8 W 0.6617 ).
